Table of Contents

What is Nagios

Preface

First release of Nagios Core was at 1999. Since this time Nagios Core project is still maintained and developed. According to this we can say that Nagios Core is one of the oldest still maintained monitoring projects.

In the case that you are looking for monitoring tool that will do anything out of the box. I personally do not think that Nagios is the right tool for you.

(To be honest I’m working with monitoring tools on enterprise level since many years, but I didn’t seen any tool that will be able to do the whole monitoring just out of the box. In the case that you know about any please let me know.)

Nagios is not solving

Based on my experiences I can say that Nagios Core is brilliant tool for monitoring in the case that you understand how it is working and you have real concept of monitoring like:
- What need to be monitored?
- How we can measure the interesting values?
- Who will get the notification?
- Do we have ticketing tool?
- Do we have the possibility for integration of Nagios with CMDB?
- Do we have delivery model for each device?
- Are we going to implement Passive monitoring?
- Are we going to implement Active polling?
- Are we going to monitor Agentless nodes?
- Are we going to use some kind of Agents?
- Do we have direct connection to all monitored devices?
- …

Scope of Nagios Core

Probably you already know that Nagios Core is developed at community as an open source project. During the time some new project have been forked from the main one. Any way most of the forked projects are still using Nagios Core as the main component, as it is compact and it is providing the main functionality that each monitoring tool has.

In the case that you are looking for:
- Compact monitoring solution.
- Based on my experiences I would say as well simple solution
- Robust and stable monitoring solution.
- That is easy to integrate with most of the tools (in the case that you are able to write basic scripts).
- That is able to extend for additional monitoring features
- When you are interested on performance of monitoring tool instead of great user GUI consuming most of the resources.
- …

In this case I would say that Nagios Core is the right tool for you.

Nagios Plugins (Checks)

Nags Core is not providing any kind of monitoring solution that can be used to run of monitoring for any device. According to this it is needed to use Nagios Plugins that are independent scripts.

It is possible to start mentioned scripts directly from CLI, as they are providing the result of monitoring with help of:
- Exit code - That will be taken over to Nagios Core as result of the monitoring check
- Output to STDOUT – That will be taken as comment related to service check

How it is working

At this point I will not go too deep in to details as this is not the right please to describe all features of Nagios. I will describe the main possibilities later so that I can go deeper in to details. On another hand I would like to provide short overview of the Nagios Core.

In general Nagios Core is:
- Scheduler
- - This is used for Active monitoring to run Check scripts delivered as Nagios Plugins

- Event broker
- - After the Check Script has finished Nagios Core is taking over the result
- - In case that we are using Passive monitoring it is possible to forward the event to Nagios

- Providing multi-tenant access
- - It is possible to manage the access to Web GUI for each User based on Host configuration (at Nagios)
- - It is possible to define different notification method for each Host or Service.

- Providing correlation and escalation
- - Nagios is able to do basic (but in most cases it is more as enough) correlation of duplicate events.
- - It is possible to enable topology based correlation of events
- - It is possible to enable Service relation based correlation of events